1. Field of the Invention
The invention relates to methods and apparatus useful for the fusion of two or more adjacent vertebrae. The present invention incorporates novel devices to facilitate placement of screws and plates to stabilize the vertebrae, and a novel system for the parallel decortication of the vertebral endplates prior to insertion of the bone graft.
2. Description of the Background
Spinal fusion is commonly used in the treatment of a number of disorders of the spinal column, both in man and animals. Spinal fusion may be used to immobilize motion segments in the spine that are diseased or require stabilization due to a number of conditions, such as trauma, spinal stenosis, disc herniation, infection, tumors, spondylolisthesis, post-laminectomy and others.
During the vertebral fusion procedure, the intervertebral disc is removed and a bone graft or other graft material is placed between the contiguous vertebrae, which may then be stabilized using a suitable implant, such as a plate. To maximize the formation of a strong callus between the fused vertebrae, the endplates of the two vertebrae are decorticated prior to insertion of the graft. Decortication is a tedious but important part of the surgical procedure. Due to the close proximity of the spinal cord and other fragile structures to the surgical site, a reliable system is needed to prepare the vertebrae for fusion, including decortication of the vertebrae and preparation of the vertebrae for the installation of the fixation plate.
There are a number of methods and devices that have been used to facilitate stabilization or repair of damage to the spinal column. There are also a number of devices which are useful to prepare the bones of the spinal column and other joints to receive implants or fixation devices. For example, artificial discs have been used to replace damaged human intervertebral discs. In one such procedure, a router guide is first used to cut elongate channels into the bodies of the two adjacent vertebrae to receive the cylindrical shaped members of the implant. In this procedure, an artificial disc is used to replace the damaged intervertebral disc, as opposed to a fusion procedure in which the disc is removed and the vertebrae are fused to each other. (U.S. Pat. No. 5,246,458). In another procedure using a disc endoprosthesis, concave surfaces are cut in the inferior and superior surfaces of the opposing vertebral bodies using a bone surface milling jig (jig not shown), prior to implantation of the endoprosthesis. (U.S. Pat. No. 5,865,846). In still another procedure using a spinal fusion implant, two cylindrical cavities are reamed immediately next to one another within the disc space. A cylindrical reamer is passed through a tubular guide laparoscopically. (U.S. Pat. No. 5,489,307 and U.S. Pat. No. 5,700,291).
In addition to methods using artificial implants in the intervetebral spaces, other devices have been developed to facilitate surgical manipulation of the vertebrae. For example, a drill and tap guide system has been used to make screw holes in vertebrae to be instrumented (U.S. Pat. No. 5,423,826). Template assemblies have been used to mark locations on the disc annulus for implantation of an interbody fusion device or introducing a working instrument (U.S. Pat. No. 5,645,549 and U.S. Pat. No. 5,785,707). In addition, a spinal transpedicle drill jig has been used to provide a safe route for drilling screw holes through the pedicles of the vertebrae (U.S. Pat. No. 4,907,577). However, none of these devices is suitable for nor provides a method or apparatus for the parallel decortication of the vertebral endplates prior to spinal fusion with a bone implant (or other bone-like implant capable of promoting fusion), and more specifically, one in which means are provided to prevent damage to the spinal cord.
With respect to other areas of the body, a number of devices have been developed to facilitate the removal of bone before implantation of a fixation device or other surgical manipulation. One such procedure utilizes an orthopedic cutting guide and bushing having a bore therethrough to prepare a femur for knee revision surgery (U.S. Pat. No. 5,735,856).
In another procedure involving the femur, a dual slide cutting guide which accommodates a milling burr is used in milling planar surfaces on a femur (U.S. Pat. No. 5,653,714). With respect to preparation of the tibia, a template may be used to mill planar surfaces on the articular surface of the tibia. A pivot arm is used to guide the depth of the cutting burr, thereby creating a planar cut in the bone surface (U.S. Pat. No. 5,344,423).
Another device for preparing the knee incorporates a saw guide, including a constrained slot for guiding the saw, useful for making cuts in the bones of the knee joint during prosthesis implantation surgery (U.S. Pat. No. 5,415,663). The foregoing devices, although quite useful in preparing the long bones of the legs, are not suitable for use on the vertebral column, and more particularly, for use in the decortication of the vertebral endplates.